Various machines, such as an industrial robot and a conveying device, which are driven with a power generator such as a motor, are controlled according to the position instruction output from a controller to a driver. Based on the position instruction, the driver calculates a torque to be output from the motor and a current value to be input to the motor, and drives the motor. As used herein, the position instruction is an instruction to designate a position after a predetermined time elapses since a current clock time in the motor or a member driven with the motor.
In recent years, there has been a research on a vibration control technology for suppressing a vibration generated in the machine by satisfying a condition (hereinafter, referred to as a vibration control condition) that does not excite the vibration of a natural frequency of the machine. In the case that the vibration control technology is applied, the controller outputs the position instruction satisfying the vibration control condition to the driver. The driver drives the motor based on the position instruction. Therefore, the vibration of the machine can be suppressed. For example, in the case that the machine is the conveying device, the conveyed matter can be conveyed while the vibration is suppressed.
Conditional expressions satisfying the vibration control condition are disclosed in various documents. Japanese Patent No. 4601659 discloses a conditional expression that generates the position instruction in which the vibration control condition is satisfied while a limiting value of maximum acceleration is satisfied. A conditional expression satisfying the vibration control condition is also disclosed in “Method for designing optimum position instruction of robot arm in consideration of vibration suppression effect” by Makoto Iwasaki and Nobuyuki Matsui, The Institute of Electrical Engineers of Japan, Transactions of Electronics, Information and Systems C, Vol. 117-C, No. 1, p 50-p 56, 1997